LaTeX

In 1985 Graham Williams began the TeX Catalogue Online project. This became a freely available and widely used resource for users of the TeX and LaTeX document typesetting system. It was one of the first XML based applications on the Internet and continues today to be an important resource for TeX and LaTeX users.

LaTeX, available on most platforms, is a freely available and open source project. It is probably the best typesetting system available, implementing professional typesetting rules to produce publication ready documents. It is a markup lanaguage though many frontends now exist to provide a graphical user interface.

Resources

EquPlus is an excellent resource for templates for numerous mathematical equations in LaTeX, MathML, and MathType.